In countries like the United States, where some states are dotted with countless lakes and many people live within easy reach of an ocean, it may be easy to assume that drinking and recreational waters are limitless. This is not the case.

In many areas of the world, water is a preciously limited resource and in some cases, water scarcity is the result of human activity. In many countries in which the water supply is scare, water is being used faster than it is being renewed, often for agriculture or to supply water for a growing population.

Agricultural overuse

About 30% of all the freshwater used in the United States and 60% of the world’s available supply of freshwater is used to grow crops. Crops require a large volume of water for production. For example, to produce 2.2 pounds (1 kilogram) of rice requires about a bathtub full of water.

Only about half of the billions of gallons of water applied to crops each year makes it back to the surface or underground. The rest is lost to the air as evaporation (the change of water from liquid to vapor) and transpiration (evaporation of water from plant leaves), leaks, and spills.

The oldest known method of irrigation (watering crops) is the most wasteful. Flooding fields with water has been used since ancient times, and still is the method of choice for crops like rice. Only about half of all the water added to a field, however, actually reaches the plant. Some modern refinements to flood irrigation have made the process less wasteful, but flood irrigation still contributes to the overuse of water.

Residential overuse

Flying over a western city like Phoenix, Arizona, can be an eye-opening experience. Sitting in the middle of a desert is an oasis (fertile area) where many houses have the distinctive blue patch in the backyard that is a swimming pool, and where hundreds of streaks of green golf course fairways stand out against the surrounding brown land. None of this would be possible without water. In naturally arid (dry areas with little annual rainfall) cities like Phoenix, the recreational use of water is a concern.

Just to the south, the city of Tucson has water police who patrol the city searching for people who break rules that are designed to prevent water waste. Infractions such as aiming a water sprinkler at the sidewalk or watering the lawn in hot periods of the day can cost a homeowner or business hundreds of dollars for a first offense.

The water used around the home in swimming pools, washing the car, washing dishes and laundry, running a lawn sprinkler, taking a bath or shower, and even flushing the toilet all use a tremendous amount of water. Statistics gathered by the government of Canada tell the tale.

Canada and the United States top the world list of average daily domestic water use. Canadian households use an average of 91 US gallons each day, while American households use just over 100 gallons. Contrast this to Israel, where water supplies are limited, which uses an average of only 36 gallons per household per day.

Overuse in North America is potentially due to the view that water is a plentiful and economical resource. Community fees that people pay to use water in North America are much lower than those in other developed countries. Germans, for example, pay an average of $2.15 per volume of water, while in the U.S., that same volume averages only 80 cents.

Community overuse

When a community gets its water supply from one or more wells or surface water sources such as a nearby lake, the amount of water that can be withdrawn can be very large. The amount of water taken out can be more than the amount of water that flows back into the source.

For example, if wells are placed too close together they can draw water from the same underground fresh water source (aquifer). This can sap water from the area much faster than if the wells are further apart and drawing water from separate aquifers.

The city of Las Vegas, Nevada, has grown from a small desert town to a city of over one million people in only about 60 years, and the population continues to skyrocket. As well, millions of people flock to the city every year for recreation. Water use in Las Vegas has increased to the point where nearby surface and underground sources of water strain to keep up with the demand.

The amount of groundwater (freshwater in rock and soil layers beneath the surface) that has been removed has caused some areas of the land near Las Vegas to sink more than 5 feet (1.5 meters) in the past 100 years.

In contrast to the sailors of a few centuries ago, humans now know that the water supply is not endless. Residential and community water use is managed in more communities throughout the developed world with the goal that the water supply is used at a rate that will ensure its availability for future generations, the ultimate goal.